1. Field of the Invention
The present invention relates to a vulcanizable composition containing a saturated elastomer having active halogen-containing cure sites and to the process of vulcanizing same. The elastomer is employed in combination with a soap/sulfur cure system and a phase transfer compound.
2. Description of the Prior Art
Elastomeric polymers have been vulcanized with sulfur in order to improve elasticity, resistance to cold flow and strength. The polymers upon vulcanization lose their tackiness, become insoluble in solvents, and their resistance to deterioration by heat and light is improved. Conventional sulfur vulcanization takes place in elastomers through unsaturation present in the elastomer molecules. The unsaturation is either present when the polymer is formed or may be introduced into the polymer molecules after the polymer is formed by methods that are known in the art.
Ethylene-vinyl acetate copolymers (EVA) may be vulcanized by introducing unsaturation by thermal or catalytic deacetylation with a protonic or Lewis acid under a vacuum of less than about 50 Torr while continuously removing acetic acid released during the deacetylation. A heated vacuum double screw extruder may be used for this purpose and olefinically unsaturated linear polymers produced as described by Bernhardt et al. in U.S. Pat. No. 4,004,069. These polymers may be cross-linked or vulcanized with sulfur according to Bernhardt et al. Ger. Offen. No. 2,413,064.
Vulcanization of saturated acrylic elastomers using a soap/sulfur cure system is also known. Mihal U.S. Pat. No. 3,458,461 discloses the vulcanization of acrylate ester elastomers containing small amounts (approx. 5% or less) of copolymerized vinyl chloroacetate (VCA) units as cure sites using cure systems comprising a soap, such as sodium or potassium stearate, in combination with elemental sulfur. Grafting of mixtures of acrylate esters and vinyl chloroacetate onto EVA elastomers and curing of the resulting grafted polymer products with soap/sulfur systems is described by Chang et al. in U.S. Pat. No. 4,202,845. Kaiserman et al. in U.S. Pat. No. 3,972,857 describe soap/sulfur vulcanization of EVA elastomers containing activated halogen atoms as sites for sulfur vulcanization. The chlorine- or bromine-containing functional groups may be incorporated into the ethylene-vinyl acetate copolymer either by copolymerization of a vinyl monomer containing the functional group with ethylene and vinyl acetate to provide a random terpolymer or by chemically modifying a copolymer of ethylene and vinyl acetate by reaction of the acetate functional group of the copolymer with a chlorine- or bromine-containing reagent. Preferably, the sites are .alpha.-chloroacetoxy groups which are substituted for some of the acetoxy groups of the EVA copolymer by acidolysis with chloroacetic acid.
Not all soaps, however, provide equivalent results in soap/sulfur vulcanization. Behrens in U.S. Pat. No. 3,939,128 has shown that soaps of higher fatty acids are four to five times less effective than the sodium or potassium salt of 2-ethylhexanoic acid for the vulcanization of acrylate ester elastomers containing VCA cure sites. Substantially higher states of cure are obtained in a shorter time with the 2-ethylhexanoate soaps than with the corresponding stearate or oleate soaps.
Since 2-ethylhexanoic acid is comparatively expensive compared to the higher fatty acids, e.g., oleic and stearic acid, which are derived from natural fats and oils and since the sodium soap of 2-ethylhexanoic acid is hygroscopic and requires handling under comparatively anhydrous conditions, it would be highly useful if higher fatty acid soaps could be effectively utilized for the vulcanization of saturated acrylic elastomers having active halogen-containing cure sites. It would be even more advantageous if comparable or superior rates of cure could be obtained utilizing the higher fatty soaps and if there were no processing problems associated therewith. These and other advantages are obtained with the compositions of the present invention and the process of vulcanizing these compositions.